Catalytic dewaxing can be used to improve the cold flow properties of a hydrocarbon feed. This can allow for production of lubricant basestocks with improved properties. Unfortunately, many conventional catalytic dewaxing methods are sensitive to the sulfur content of a feedstock. Using such conventional dewaxing methods, the sulfur and/or nitrogen content of a feedstock is reduced to low levels, such as less than 100 wppm of sulfur, prior to catalytic dewaxing. Conventionally, the reduction of sulfur and/or nitrogen levels is required in order to maintain catalyst activity and achieve desired yields of lube basestock.
U.S. Pat. No. 5,951,848 provides a method for treating a hydrocarbon feedstock by first exposing the feedstock to a high activity hydrotreating catalyst to reduce the levels of, for example, nitrogen, sulfur, and aromatics. The hydrotreated feed is then dewaxed using a dewaxing catalyst, such as ZSM-23, ZSM-35, or ZSM-48.
U.S. Pat. No. 7,077,948 provides a method for catalytic dewaxing. The method includes treating a feed having at least 500 ppm sulfur with a dewaxing catalyst that includes an aluminosilicate zeolite. The dewaxing catalyst also includes a binder that is essentially free of aluminum. The method discloses that catalytic dewaxing occurs prior to hydrotreating.
U.S. Published Patent Application 2009/0005627 describes a method for integrated hydroprocessing of feeds having varying wax contents. The method includes operating a reaction system in a blocked mode, where feeds having differing wax contents can be processed in a single reaction train by varying the reaction temperature.
There is a need for improved methods of dewaxing lubricant feedstocks having varying levels of sulfur contaminants to form lubricant basestocks without the need for separating such sulfur contaminants prior to the catalytic dewaxing step of the process.